Nearly all of the mechanisms to generate sliding friction torque or click torque with the rotating shaft of a conventional biaxial hinge generate this torque in ways: a corrugated spring is directly held against a sliding member, or a cam is held down with a coned disk spring or other such leaf spring (see Japanese Patent Publication 2002-155923).
FIG. 10 illustrates an example of a conventional biaxial hinge structure. A leaf spring 103 formed in a corrugated shape is attached to one end of a rotating shaft 102 disposed through a stamped opening/closing shaft 101, fixing members 104 are rotatably attached to the both ends of an opening/closing shaft, and rotational torque is generated by pressing a friction member 105 attached to the opening/closing haft against the leaf spring 103.
Since torque is generated by utilizing the repulsive force of a leaf spring to press on a friction member, a conventional hinge has problems that include wear of the friction member 105, looseness and chatter caused by deformation (permanent set in fatigue) of the leaf spring 103, poor durability, and so forth. Torque fluctuations and decreased durability over time not only diminish the quality of the device, but also lead to malfunctions. With today's biaxial hinges, more emphasis is placed on ease of operation and tactile feedback during rotation and opening/closing than with past products, and there is a great need for a hinge that is smaller and more lightweight, has better durability, and retains its torque value better.
Also, because a leaf spring or friction member is disposed near the center of the rotating shaft, in conventional hinges, it is difficult to make a hole in the rotating shaft center through which wires or the like can be passed to electrically connect the members linked by the biaxial hinge. The wires therefore have to be routed on the outside of the rotating shaft, the result of which is an increase in the overall size including the wiring.